The use of chemically resistant fibers to form complex shapes or act as reinforcement has long been known. In the art, there are known organic polymer fibers such as extruded polytetrafluoroethylene fibers, inorganic fibers such as carbon fibers, naturally occurring fibers such as spun cotton, and mixes of ceramics and fibers (floor tile). Also, there are materials made of mixes of inorganic fibers and organic polymer fibers, where the organic polymer fibers act as a "glue" to hold the inorganic fibers together. For instance, some literature shows inorganic fibers such as potassium titanate or zirconia used together with polytetrafluoroethylene as a "glue" in the manufacture of sheets, filters, or other finished products. However, this art merely shows the materials used with each other, but not formed into an inorganic-polymer composite fiber as in the instant invention.
A specific example of this art is Canadian Patent 834,895, which discloses a battery separator made of potassium titanate as the inorganic material used with polytetrafluoroethylene as the organic material. Another example of this art is U.S. Pat. No. 3,713,890, which discloses a battery separator made of zirconia as the inorganic material used with polytetrafluroethylene as the organic material. In addition, an article entitled "New separators for Nickel-Cadmium Cells" in the Journal, Proc. of the Intersociety Energy Conversion Conference, 16th, XI, (1981). discloses a battery separator of Zircartm (zirconia fabric number ZYW15.TM. manufactured by Zircar Products, Inc.) reinforced with polytetrafluoroethylene.
Also, it has been known to take an isotropic carbon fiber and press it together with polytetrafluoroethylene for use as artificial tendons in human bodies, as disclosed in U.S. Pat. No. 3,992,725. This patent also discloses that zirconia fiber may be employed instead of carbon fiber.
Also known in the prior art are gaskets and bearings commonly made by molding a blend of inorganic fiber and polymer powder. Typical compositions include 40-80% polymer blends of inorganic and powdered polymer. These blends are compressed and heated to form the final product. The blend precursors are less than 100 microns in diameter, although they may be preblended into larger particles before molding.
In all of these prior art examples, the mixture of polymer and inorganic does not exhibit any non-uniform fiber morphology. According to the prior art, the concurrent use of a polymer and an inorganic does not require the formation of any non-isotropic intermediate, composite fibers. In other words, a composite fiber is not formed, but rather the polymer is simply used "to glue" the inorganic fiber together.
It has also been proposed to incorporate extremely finely divided particles into molten thermoplastics. The resulting thermoplastics can then be shaped. For example, U.S. Pat. No. 4,126,536 discusses the addition of sub-micron-sized particles, such as of titanium dioxide to such a molten substance. In shaping, the resultant. material can be extruded through a die and the extrudate broken into fibers. However, the resulting product has the particles incorporated in the fiber, i.e., encapsulated therein, thereby losing the surface character of the fine particles within the polymer.